Process for producing spherical polysilsesquioxane particles

Abstract

Spherical polysilsesquioxane particles are prepared by reacting trialkoxysilanes of formula, (I) RSi(OR 1 ) 3   (I), where R represents a C 1-16 hydrocarbon radical whose carbon chain may be interrupted by nonadjacent —O— groups, R 1 represents a C 1-4 alkyl radical, with acidified water having a pH≤6 with stirring to produce a hydrolysate, in a second step mixing the hydrolysate with a solution of NaOH and/or KOH, and in a third step storing the mixture is stored for at least 8 h before isolating polysilsesquioxane particles thus formed.

The invention claimed is: 
     
       1. A process for producing spherical polysilsesquioxane particles, comprising:
 a) in a first step, reacting at least one trialkoxysilane of the formula, (I)
   RSi(OR 1 ) 3   (I),
 
 
 
       in which 
       R represents a hydrocarbon radical having 1 to 16 carbon atoms whose carbon chain is optionally interrupted by nonadjacent —O— groups, and 
       R 1  represents a C 1 - to C 4 -alkyl radical, 
       with acidified water having a pH of not more than 6 with stirring to afford a hydrolysate,
 b) in a second step, mixing the hydrolysate with a solution comprising NaOH, KOH, or a mixture thereof, and 
 c) in a third step, storing the mixture in the substantial absence of agitation for at least 8 h, forming spherical polysilsesquioxane particles, before isolating the polysilsesquioxane particles. 
 
     
     
       2. The process of  claim 1 , in which R is an ethyl radical or methyl radical. 
     
     
       3. The process of  claim 1 , in which R 1  is an ethyl radical or methyl radical. 
     
     
       4. The process of  claim 2 , in which R 1  is an ethyl radical or methyl radical. 
     
     
       5. The process of  claim 1 , in which the reaction to afford the hydrolysate in step b) is effected at a pH of 4.5 to 2. 
     
     
       6. The process of  claim 4 , in which the reaction to afford the hydrolysate in step b) is effected at a pH of 4.5 to 2. 
     
     
       7. The process of  claim 1 , in which the temperature of the reaction in step a) is 0° C. to 60° C. 
     
     
       8. The process of  claim 1 , in which in the first step, 5 to 43 parts by weight of trialkoxysilane are added per 100 parts by weight of water. 
     
     
       9. The process of  claim 1 , in which in the second step a solution of alkali metal hydroxide in water or in an alkanol having 1 to 3 carbon atoms is employed as the solution comprising KOH, NaOH, or a mixture thereof. 
     
     
       10. The process of  claim 1 , in which sufficient solution of alkali metal hydroxide is added to obtain a pH of 6.5 to 9.5 following addition of alkali metal hydroxide. 
     
     
       11. The process of  claim 1 , in which the temperature of the addition of alkali metal hydroxide in the second step b) is 10° C. to 40° C. 
     
     
       12. The process of  claim 1 , in which in the third step c) the mixture is stored for at least 14 h before the polysilsesquioxane particles are isolated. 
     
     
       13. The process of  claim 1 , in which after the third step c) the particles are isolated by filtration or centrifugation. 
     
     
       14. The process of  claim 1 , wherein the mixture in step c) is not moved until prior to isolation of the polysilsesquioxane particles. 
     
     
       15. The process of  claim 1 , wherein the isolated polysilsesquioxane particles have an average sphericity of ≥0.6 as measured in accordance with DIN EN 13503-2, p. 37, annex B.3. 
     
     
       16. The process of  claim 1 , wherein the isolated polysilsesquioxane particles have an average sphericity of ≥0.7 as measured in accordance with DIN EN 13503-2, p. 37, annex B.3. 
     
     
       17. The process of  claim 1 , wherein the isolated polysilsesquioxane particles have an average roundness of ≥0.6 as measured in accordance with DIN EN 13503-2, p. 37, annex B.3. 
     
     
       18. The process of  claim 1 , wherein the isolated polysilsesquioxane particles have an average roundness of ≥0.7 as measured in accordance with DIN EN 13503-2, p. 37, annex B.3. 
     
     
       19. The process of  claim 1 , wherein the isolated polysilsesquioxane particles are fluidizable into a flowable state.